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SUPERFICIAL STRUCTURES OF NECK: CERVICAL REGIONS Congenital Torticollis Torticollis (L. tortus, twisted + L. collum, neck) is a contraction or shortening of the cervical muscles that produces twisting of the neck and slanting of the head. The most common type of torticollis (wry neck) results from a fibrous tissue tumor (L. fibromatosis colli) that develops in the SCM before or shortly after birth. The lesion, like a normal unilateral SCM contraction, causes the head to tilt toward, and the face to turn away from, the affected side (Fig. B8.1). When torticollis occurs prenatally, the abnormal position of the infant's head usually necessitates a breech delivery. Occasionally, the SCM is injured when an infant's head is pulled too much during a difficult birth, tearing its fibers (muscular-torticollis) (Behrman et al., 2000). A hematoma (localized mass of extravasated blood) occurs that may develop into a fibrotic mass that entraps a branch of the spinal accessory nerve (CN XI) and thus denervates part of the SCM. The stiffness and twisting of the neck results from fibrosis and shortening of the SCM. Surgical release of the SCM from its inferior attachments to the manubrium and clavicle inferior to the level of CN XI may be necessary to enable the person to hold and rotate the head normally. P.1008 FIGURE B8.1. Spasmodic Torticollis Cervical dystonia (abnormal tonicity of the cervical muscles), commonly known as spasmodic torticollis, usually begins in adulthood. It may involve any bilateral combination of lateral neck muscles, especially the SCM and trapezius. Characteristics of this disorder are sustained turning, tilting, flexing, or extending of the neck. Shifting the head laterally or anteriorly can occur involuntarily (Fahn et al., 2005). The shoulder is usually elevated and displaced anteriorly on the side to which the chin turns. Subclavian Vein Puncture The right or left subclavian vein is often the point of entry to the venous system for central line placement, such as a Swan-Ganz catheter. Central lines are inserted to administer parenteral (venous nutritional) fluids and medications and to measure central venous pressure. In an infraclavicular subclavian vein approach, the administrator places the thumb of one hand on the middle part of the clavicle and the index finger on the jugular notch in the manubrium (Fig. B8.2). The needle punctures the skin inferior to the thumb (middle of the clavicle) and is advanced medially toward the tip of the index finger (jugular notch) until the tip enters the right venous angle, posterior to the sternoclavicular joint. Here the internal jugular and subclavian veins merge to form the brachiocephalic vein. If the needle is not inserted carefully, it may puncture the pleura and lung, resulting in pneumothorax. Furthermore, if the needle is inserted too far posteriorly, it may enter the subclavian artery. When the needle has been inserted correctly, a soft, flexible catheter is inserted into the subclavian vein, using the needle as a guide. Right Cardiac Catheterization For right cardiac catheterization (to take measurements of pressures in the right chambers of the heart), puncture of the IJV can be used to introduce a catheter through the right brachiocephalic vein into the superior vena cava (SVC) and the right side of the heart. Although the preferred route is through the IJV or the subclavian vein, it may be necessary in some patients to use the EJV. This vein is not ideal for catheterization because its angle of junction with the subclavian vein makes passage of the catheter difficult. Prominence of External Jugular Vein The EJV may serve as an “internal barometer.” When venous pressure is in the normal range, the EJV is usually visible above the clavicle for only a short P.1009 distance. However, when venous pressure rises (e.g., as in heart failure), the vein is prominent throughout its course along the side of the neck. Consequently, routine observation of the EJVs during physical examinations may give diagnostic signs of heart failure, SVC obstruction, enlarged supraclavicular lymph nodes, or increased intrathoracic pressure. Severance of External Jugular Vein If the EJV is severed along the posterior border of the SCM where it pierces the roof of the lateral cervical region (e.g., by a knife slash), its lumen is held open by the tough investing layer of deep cervical fascia, and the negative intrathoracic pressure air will suck air into the vein. This action produces a churning noise in the thorax and cyanosis (a bluish discoloration of the skin and mucous membranes resulting from an excessive concentration of reduced hemoglobin in the blood). A venous air embolism produced in this way will fill the right side of the heart with froth, which nearly stops blood flow through it, resulting in dyspnea. The application of firm pressure to the severed jugular vein until it can be sutured will stop the bleeding and entry of air into the blood. Lesions of Spinal Accessory Nerve (CN XI) Lesions of the spinal accessory nerve are uncommon. CN XI may be damaged by: Penetrating trauma, such as a stab or bullet wound. Surgical procedures in the lateral cervical region. Tumors at the cranial base or cancerous cervical lymph nodes. Fractures of the jugular foramen where CN XI leaves the cranium. Although contraction of one SCM turns the head to one side, a unilateral lesion of CN XI usually does not produce an abnormal position of the head. However, people with CN XI damage usually have weakness in turning the head to the opposite side against resistance. Lesions of the CN XI produce weakness and atrophy of the trapezius, impairing neck movements. Unilateral paralysis of the trapezius is evident by the patient's inability to elevate and retract the shoulder and by difficulty in elevating the upper limb superior to the horizontal level. The normal prominence in the neck produced by the trapezius is also reduced. Drooping of the shoulder is an obvious sign of CN XI injury. During extensive surgical dissections in the lateral cervical region—for example, during removal of cancerous lymph nodes—the surgeon isolates CN XI to preserve it, if possible. An awareness of the superficial location of this nerve during superficial procedures in the lateral cervical region is important because CN XI is the most commonly iatrogenic nerve injury (G. iatros, physician or surgeon). Severance of Phrenic Nerve, Phrenic Nerve Block, and Phrenic Nerve Crush Severance of a phrenic nerve results in paralysis of the corresponding half of the diaphragm (see the blue box “Paralysis of the Diaphragm” on p. 85). A phrenic nerve block produces a short period of paralysis of the diaphragm on one side (e.g., for a lung operation). The anesthetic is injected around the nerve where it lies on the anterior surface of the middle third of the anterior scalene muscle. A surgical phrenic nerve crush (e.g., compressing the nerve injuriously with forceps) produces a longer period of paralysis (sometimes for weeks after surgical repair of a diaphragmatic hernia). If an accessory phrenic nerve is present, it must also be crushed to produce complete paralysis of the hemidiaphragm. Nerve Blocks in Lateral Cervical Region For regional anesthesia before neck surgery, a cervical plexus block inhibits nerve impulse conduction. The anesthetic agent is injected at several points along the posterior border of the SCM, mainly at the junction of its superior and middle thirds, the nerve point of the neck (Figs. 8.8 and 8.13A). Because the phrenic nerve supplying half the diaphragm is usually paralyzed by a cervical nerve block, this procedure is not performed on persons with pulmonary or cardiac disease. For anesthesia of the upper limb, the anesthetic agent in a supraclavicular brachial plexus block is injected around the supraclavicular part of the brachial plexus. The main injection site is superior to the midpoint of the clavicle. Injury to Suprascapular Nerve The suprascapular nerve is vulnerable to injury in fractures of the middle third of the clavicle. Injury of this nerve results in loss of lateral rotation of the humerus at the glenohumeral joint. Consequently the relaxed limb rotates medially into the waiter's tip position (see Fig. B6.12B). The ability to initiate abduction of the limb is also affected. Ligation of External Carotid Artery Ligation of an external carotid artery is sometimes necessary to control bleeding from one of its relatively inaccessible branches. This procedure decreases blood flow through the artery and its branches but does not eliminate it. Blood flows in a retrograde (backward) direction into the artery from the external carotid artery on the other side through communications between its branches (e.g., those in the face and scalp) and across the midline. When the external carotid or subclavian arteries are ligated, the descending branch of the occipital artery provides the main collateral circulation, anastomosing with the vertebral and deep cervical arteries. P.1010 Surgical Dissection of Carotid Triangle The carotid triangle provides an important surgical approach to the carotid system of arteries. It also provides access to the IJV, the vagus and hypoglossal nerves, and the cervical sympathetic trunk. Damage or compression of the vagus and/or recurrent laryngeal nerves during surgical dissection of the carotid triangle may produce an alteration in the voice because these nerves supply laryngeal muscles. Carotid Occlusion and Endarterectomy Atherosclerotic thickening of the intima of the internal carotid artery may obstruct blood flow. Symptoms resulting from this obstruction depend on the degree of obstruction and the amount of collateral blood flow to the brain and structures in the orbit from other arteries. A partial occlusion of the internal carotid may cause a transient ischemic attack (TIA), a sudden focal loss of neurological function (e.g., dizziness and disorientation) that disappears within 24 hr. Arterial occlusion may also cause a minor stroke, a loss of neurological function such as weakness or sensory loss on one side of the body that exceeds 24 hr but disappears within 3 weeks. Obstruction of blood flow can be observed in a Doppler color study (Fig. B8.3A). A Doppler is a diagnostic instrument that emits an ultrasonic beam and detects its reflection from moving fluid (blood) in a manner that distinguishes the fluid from the static surrounding tissue, providing information about its pressure, velocity, and turbulence. Carotid occlusion, causing stenosis (narrowing) in otherwise healthy persons (Fig. B8.3B) can be relieved by opening the artery at its origin and stripping off the atherosclerotic plaque with the intima. This procedure is called carotid endarterectomy. After the operation, drugs that inhibit clot formation are administered until the endothelium has regrown. Because of the relations of the internal carotid artery, there is risk of cranial nerve injury during the procedure involving one or more of the following nerves: CN IX, CN X (or its branch, the superior laryngeal nerve), CN XI, or CN XII (Fig. 8.21). Carotid Pulse The carotid pulse (“neck pulse”) is easily felt by palpating the common carotid artery in the side of the neck, where it lies in a groove between the trachea and the infrahyoid muscles. It is usually easily palpated just deep to the anterior border of the SCM at the level of the superior border of the thyroid cartilage. It is routinely checked during cardiopulmonary resuscitation (CPR). Absence of a carotid pulse indicates cardiac arrest. Carotid Sinus Hypersensitivity In people with carotid sinus hypersensitivity (exceptional responsiveness of the carotid sinuses in various types of vascular disease), external pressure on the carotid artery may cause slowing of the heart rate, a fall in blood pressure, and cardiac ischemia resulting in fainting (syncope). In all forms of syncope, symptoms result from a sudden and critical decrease in cerebral perfusion (Hirsch et al, 2005). Consequently, this method of checking the pulse is not recommended for people with cardiac or vascular disease. Alternate sites, such as the radial artery at the wrist, should be used to check pulse rate in people with carotid sinus hypersensitivity. FIGURE B8.3. Role of Carotid Bodies The carotid bodies are in an ideal position to monitor the oxygen content of the blood before it reaches the brain. A decrease in PO2 (partial pressure of oxygen), as occurs at high altitudes or in pulmonary disease, activates the aortic and carotid chemoreceptors, increasing alveolar ventilation. The carotid bodies also respond to increased carbon dioxide (CO2) tension or free hydrogen ions in the blood. The glossopharyngeal nerve (CN IX, perhaps with involvement of the vagus nerve) conducts the information centrally, resulting in reflexive stimulation of the respiratory centers of the brain that increase the depth and rate of breathing. The pulse rate and blood pressure also increase. With the increased ventilation and circulation, more oxygen is taken in and the concentration of CO2 is reduced accordingly. P.1011 Internal Jugular Pulse Although pulsations are most commonly associated with arteries, pulsations of the internal jugular vein can provide information about heart activity corresponding to electrocardiogram (ECG) recordings and right atrial pressure. The IJV pulse is not palpable in the same manner as arterial pulses; however, the vein's pulsations are transmitted through the surrounding tissue and may be observed beneath the SCM superior to the medial end of the clavicle. Because there are no valves in the brachiocephalic vein or the superior vena cava, a wave of contraction passes up these vessels to the inferior bulb of the IJV. The pulsations are especially visible when the person's head is inferior to the lower limbs (the Trendelenburg position). The internal jugular pulse increases considerably in conditions such as mitral valve disease (see Chapter 1), which increases pressure in the pulmonary circulation and the right side of the heart. The right IJV runs a straighter, more direct course to the right atrium than does the left; thus it is the one that is examined (Swartz, 2006). Internal Jugular Vein Puncture A needle and catheter may be inserted into the IJV for diagnostic or therapeutic purposes. The right internal jugular is preferable because it is usually larger and straighter. During this procedure, the clinician palpates the common carotid artery and inserts the needle into the IJV just lateral to it at a 30° angle, aiming at the apex of the triangle between the sternal and the clavicular heads of the SCM, the lesser supraclavicular fossa (Fig. B8.4). The needle is then directed inferolaterally toward the ipsilateral nipple. The Bottom Line SUPERFICIAL STRUCTURES OF NECK: CERVICAL REGIONS Sternocleidomastoid and trapezius: The SCM and trapezius muscles share their origins from a common embryologic source, innervation by the spinal accessory nerve (CN XI), enclosure by the investing layer of deep cervical fascia, a linear superior attachment to the cranial base, and an inferior attachment to the pectoral girdle. ♦ Their superficial masses and palpable borders provide the basis for describing the regions of the neck. ♦ The SCM produces multiple movements of the head and neck. ♦ The trapezius causes multiple movements of the scapula, depending on whether the muscles act unilaterally or bilaterally and independently or in conjunction with concentric or eccentric contraction of other muscles. Lateral cervical region: The lateral cervical region is bounded by the SCM, trapezius, and middle third of the clavicle, with a muscular floor formed by the lateral deep cervical muscles. ♦ It is subdivided by the diagonally placed inferior belly of the omohyoid. ♦ Most apparent within the superior occipital triangle is the lower half of the external jugular vein. ♦ Most important clinically is the superficially located spinal accessory nerve (CN XI). ♦ In the inferior and much smaller omoclavicular triangle, the brachial plexus emerges between the middle and anterior scalene muscles, the latter of which is crossed anteriorly by the phrenic nerve. ♦ Superior to the brachial plexus, and in the same plane, is the cervical plexus. ♦ The cutaneous branches of this plexus emerge from the midpoint of the posterior border of the SCM and radiate toward the scalp, auricle, anterior neck, and shoulder. Anterior cervical region: The anterior cervical region is inferior to the body of the mandible, extending anteriorly from the SCM to the midline. ♦ The bellies of the digastric, the anterior belly of the omohyoid, and the hyoid subdivide the region into smaller triangles. ♦ The submental triangle is superficial to the floor of the mouth. ♦ The submandibular triangle, superior to the digastric bellies, is occupied by the submandibular salivary gland and submandibular lymph nodes. ♦ The facial artery, coursing within this triangle, is palpable as it emerges from it and crosses the body of the mandible. ♦ The carotid triangle, between the posterior belly of the digastric, inferior belly of the omohyoid, and SCM, includes much of the carotid sheath and related structures, including the bifurcation of the common carotid, the carotid sinus and body, and the initial branches of the external carotid artery. ♦ The muscular triangle is formed and occupied by the infrahyoid muscles.